DTD Question

[Ronald Bourret]

Samuel R. Blackburn wrote:

> I just attended a briefing about XML. One of the things
> that struck me was, if I understand the presenter, DTD
> thinks the world is flat. Is it possible for DTD to describe
> elements of the same name but have different meaning?
> 
> Consider the following:
> 
> <NAME>
>   <FIRST>Sam</FIRST>
>   <LAST>Blackburn</LAST>
> </NAME>
> <ROUTE>
>    <FIRST>99.409</FIRST>
>    <LAST>2091.7785</LAST>
> </ROUTE>
> 
> Is it possible in DTD to say that NAME.FIRST is a string
> and ROUTE.FIRST is a number?

No.  DTDs cannot describe the data type of non-attribute data.  It is always character.

There are various schema languages floating around, some of which (DCD, SOX), support data types. However, these do not support multiple types for the same element -- that is, you would need FIRST1 and FIRST2 in your example.

The only way to apply the constraints you want is in the application.  This is possible in your example because the parents of FIRST are different in each case.

-- Ron Bourret

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